ECR Plasma Research Articles

Light ion source for proton/deuteron production at CEA Saclay for the Spiral2 project

The production of rare radioactive ion beam (RIB) far from the valley of stability is one of the final purposes of the Spiral2 facility in Caen. The RIB will be produced by impinging a deuteron beam onto a carbon sample to produce a high neutron flux, which will interact with a uranium target. The primary deuteron beam is produced by an ion source based on ECR plasma generation. The deuteron source and the low energy beam transport (LEBT) has been assembled and tested at CEA Saclay. Diagnostics from other laboratories were implemented on the LEBT in order to characterize the deuteron beam produced and compare it to the initial simulations. The ion source has been based on a SILHI-type source, which has demonstrated good performances in pulsed and continuous mode, and also a very good reliability on long term operation. The 5 mA of deuteron beam required at the RFQ entrance is extracted from the plasma source at the energy of 40 kV. After a brief description of the experimental set-up, this article reports on the first beam characterization experiments.

Detection of Vertical Charge Separation Current in a Toroidal ECR Plasma by Radially Aligned Multi-Electrodes

In plasmas immersed in the toroidal field Bφ, electrons drift downward while ions drift upward due to the field gradient and curvature (Bφ > 0 is assumed). The plasma is usually bounded at the top and bottom by the conducting vessel walls. The same amount of current must flow into and out from the walls at the top and bottom, respectively, to complete the current circulation via the vacuum vessel. In an ECR plasma in the LATE device radial profiles of vertical charge separation currents have been for the first time measured by radially aligned multi-electrodes fabricated at the top and bottom. Both the profiles at the top and bottom are nearly the same as the profile 2Pe/RBφ in the plasma as theoretically predicted. Current characteristics upon the sweep of external voltage onto the top ion collectors reveal that the current is due to inflow of ions with no secondary electron emission. c © 2012 The Japan Society of Plasma Science and Nuclear Fusion Research

Simulation of the Formation of an Ion Beam by Extraction From a Magnetically Confined Plasma

A computational simulation of the formation of an ion beam extracted from a magnetically confined ECR plasma is made. The first simulation stage consists of calculating of the electrostatic field produced by an extraction system. The extraction system is composed of three cylindrically hollow symmetrical electrodes and its respective shielding box. For the purpose of calculating the extraction and focalization electrostatic field, a finite-difference algorithm that solves Laplace equation within the ion propagation volume and allows studying the dependency of the electrostatic field on the geometrical configuration of the extraction system is developed. The second stage consists in calculating the electric and magnetic fields due to extracted ions themselves by solving Poisson equation using the fast Fourier transform technique based on a high-order difference approximation with identity expansion scheme. Finally, an algorithm based on Boris integration scheme to calculate ion trajectories with the objective of simulating the movement on an ion beam due to the field generated by electrodes and beam itself is developed. Based upon the results obtained, the search for an optimized ion extraction system from a 14-GHz ECR ion source is begun. Preliminary configurations are obtained and shown.

Influence of the pulsating electric field on the ECR heating in a nonuniform magnetic field

According to a computer simulation, the randomized pulsating electric field can strongly influence the ECR plasma heating in a nonuniform magnetic field. It has been found out that the electron energy spectrum is shifted to the high energy region. The obtained effect is intended to be used in the ECR sources for effective X-ray generation.

Visible Plume From a Low-Power ECR Waveguide Plasma Cathode for Electric Propulsion Systems

A waveguide ECR plasma cathode is being investigated as a long-lived alternative to thermionic emitter-based electron sources for ion beam neutralization in electric propulsion systems. The present device can deliver up to 4.2 A of electron current, on argon or xenon, with low power consumption and high gas utilization.

Properties study of silicon carbide thin films prepared by electron cyclotron resonance plasma technology

Silicon carbide films were deposited at two deposition temperatures 350 °C and 450 °C by means of ECR plasma reactor with two gas mixtures: (1) gas mixture, SiH4 (5 sccm), CH4 (14 sccm), Ar (6 sccm), NH3 (2 sccm) and (2) gas mixture SiH4 (5 sccm), CH4 (14 sccm), H2 (6 sccm), NH3 (2 sccm). The concentration of species in the SiC films was determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analytical method simultaneously. Chemical compositions were analyzed by infrared (IR) spectroscopy. Photoluminescence (PL) spectra were measured at 300 K. The RBS and ERD results showed that the concentrations of Si and C in the films are practically the same. The concentration of hydrogen decreased from 30 to 22 at.% with an increasing sample deposition temperature. The films contain a small amount of nitrogen and oxygen. IR results showed the presence of Si-C, Si-N, Si-H, C-H and Si-O bonds. PL results showed the decrease of the PL intensity with an increasing sample deposition temperature.

(Invited) MOS Interface Control Technologies for III-V/Ge Channel MOSFETs

In order to realize high current drive and low supply voltage CMOS, attentions have recently been paid to III-V and Ge channels. However, one of the most critical issues for realizing Ge/III-V MOSFETs is gate insulator formation with superior MOS interface quality on Ge/III-V. In this paper, we focus on the possible solutions for gate stack technologies on Ge/III-V. As for Ge, GeO2/Ge interfaces have been regarded as promising. We have succeeded in thin EOT gate stacks with Ge oxide interfacial layers by using ECR plasma post oxidation. The high quality Al2O3/GeOx/Ge gate stacks were fabricated by exposing the ALD Al2O3/Ge structures to ECR oxygen plasma. As for InGaAs channels, we have also proposed a novel interfacial control technology utilizing InGaAs surface nitridation by ECR nitrogen plasma and successive post metallization annealing. This interfacial layer is shown to reduce Dit down to low order of 1011 cm-2eV-1.

Development of a 14.5 GHz Electron Cyclotron Resonance Ion Source at KAERI

A 14.5 GHz ECRIS has been designed and fabricated at KAERI (Korea Atomic Energy Research Institute) to produce multi-charged ion beam (especially for C 6+ ion beam) for medical application. The magnet system has cupper conductor solenoid coils and a permanent magnet hexapole. A welded tube with aluminium and stainless steel is used for an ECR plasma chamber to improve the production of secondary electron. A Krystron supplies microwave energy to the plasma. A movable beam extractor with 8 mm aperture covers different species and different charge numbers of the beam. Fabrication and initial experimental results on ECR plasma are discussed in this paper.

Carbon Nanoparticle/Hydrogenated Amorphous Carbon Composite Thin Films Formed in ECR Plasma

AbstractComposite thin films are deposited from acetylene in a microwave multipolar plasma excited at distributed electron cyclotron resonance in one single process. The composite consists of carbon‐based nanoparticles embedded in a hydrogenated amorphous matrix. Effects of plasma duration and microwave power on the composite thin film are described along with the powder growth mechanisms. Indeed, two types of nanoparticles are formed: pure graphite‐like and graphite‐like shell with a metallic core. The first type grows from recombinations in the plasma phase, while core‐shelled starts from a metallic core generated from the reactor walls. These metallic clusters can be heated while immersed in the plasma which leads to catalytic growth of powders. magnified image

Magnetoelectric heating in the ECR plasma

The magnetoelectric heating is investigated on an ECR plasma device. The ion temperatures are measured by ion sensitive probe (ISP) before and after magnetoelectric heating. The influences of bias voltage of electrical ring, magnet field and pressure on ion temperature and the efficiency of ion heating are studied. The results indicate that the whole heating of the plasma is accomplished through the magnetoelectric heating of the ions in the sheath of the electric ring and the radial transport of the heated ions. The ion temperature in the axial area increases with the bias voltage of electric ring, and their relationship is nonlinear. The ion temperature increases more than 20 eV when the bias voltage is 1000 V. A heating efficiency is achieved to be as high as 2%2.5% and increases with the bias voltage increasing. The magnetic field strength plays an important role in the limitation and heating of the ions. The efficiency of the magnetoelectric heating increases with the increase of the magnetic field strength when the magnetic field strength changes from 6.310-2T to 8.710-2T. The efficiency of the magnetoelectric heating increases with the pressure decreasing when the pressure chenges in a range of 0.020.8Pa.

Dissociative Excitation Process of BrCN in the ECR Plasmas of Rare Gases

Dissociative Excitation Process of BrCN in the ECR Plasmas of Rare Gases

Recent Developments on High-Power Gyrotrons—Introduction to This Special Issue

Gyrotrons with output powers of several 100 kW are mainly used as high-power millimeter (mm)-wave sources for electron cyclotron resonance heating (ECRH), electron cyclotron current drive (ECCD), stability control and diagnostics of magnetically confined plasmas for generation of energy by controlled thermonuclear fusion. Other applications include ECR ion sources, materials processing and plasma chemistry, high-resolution Doppler radar, radar ranging and imaging in atmospheric and planetary science, active denial systems, as well as detection of concealed radioactive materials. The present review summarizes the status of recent developments on high-power gyrotrons and introduces this Special Issue on Gyrotrons.

Convective plasma stability consistent with MHD equilibrium in magnetic confinement systems with a decreasing field

A study is made of the convective (interchange, or flute) plasma stability consistent with equilib� rium in magnetic confinement systems with a magnetic field decreasing outward and large curvature of mag� netic field lines. Algorithms are developed which calculate convective plasma stability from the Kruskal- Oberman kinetic criterion and in which the convective stability is iteratively consistent with MHD equilib� rium for a given pressure and a given type of anisotropy in actual magnetic geometry. Vacuum and equilibrium convectively stable configurations in systems with a decreasing, highly curved magnetic field are calculated. It is shown that, in convectively stable equilibrium, the possibility of achieving high plasma pressures in the central region is restricted either by the expansion of the separatrix (when there are large regions of a weak magnetic field) or by the filamentation of the gradient plasma current (when there are small regions of a weak magnetic field, in which case the pressure drops mainly near the separatrix). It is found that, from the stand� point of equilibrium and of the onset of nonpotential ballooning modes, a kinetic description of convective stability yields better plasma confinement parameters in systems with a decreasing, highly curved magnetic field than a simpler MHD model and makes it possible to substantially improve the confinement parameters for a given type of anisotropy. For the Magnetor experimental compact device, the maximum central pressure consistent with equilibrium and stability is calculated to be as high as β ~ 30%. It is shown that, for the anisot� ropy of the distribution function that is typical of a background ECR plasma, the limiting pressure gradient is about two times steeper than that for an isotropic plasma. From a practical point of view, the possibility is demonstrated of achieving better confinement parameters of a hot collisionless plasma in systems with a decreasing, highly curved magnetic field than those obtained with the simplest MHD description.

Collisionless Drift Waves Ranging from Current‐Driven, Shear‐Modified, and Electron‐Temperature‐Gradient Modes

AbstractThe specific history of collisionless drift waves is marked by focusing upon current‐driven, shear‐modified, and electron‐temperature‐gradient modes. Studies of current‐driven collisionless drift waves started in 1977 using the Innsbruck Q machine and was continued over 30 years until 2009 with topics such as plasma heating by drift waves in fusion‐oriented confinement and space/astrophysical plasmas. Superposition of perpendicular flow velocity shear on parallel shear intensively modifies the drift wave characteristics through the variation of its azimuthal structure, where the parallel‐shear driven instability is suppressed for strong perpendicular shears, while hybrid‐ion velocity shear cause unexpected stabilization of the parallel‐shear‐modified drift wave. An electron temperature gradient can be formed easily by control of thermionic electron superimposed on ECR plasma, and is found to excite low‐frequency fluctuation in the range of drift waves (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

ECR heating power modulation as a means to ease the overcoming of the radiation barrier in fusion devices

A method is proposed to ease the overcoming of the impurity radiation barrier during current drive in tokamaks, as well as in alternative fusion and plasmochemical systems with ECR plasma heating. The method is based on the fact that the dependence of the ionization rate on the electron temperature is strongly nonlinear and the dependence of the recombination rate on the latter is weaker. The result is that, during temperature oscillations, the effective temperature for ionization-recombination processes is higher than that in a steady state, so the ionization equilibrium is shifted and strongly emitting ions are stripped more rapidly. Thereby, ECR plasma heating in the initial discharge stage can be made more efficient by modulating the heating power at a low frequency. The evolution of the electron temperature in a homogeneous hydrogen plasma with a carbon impurity and in small ISX-scale tokamaks is simulated numerically, as well as the evolution of the electron and ion temperatures and of the current during discharge startup in the ITER device. Numerical simulations of the effect of modulation of the ECR heating power on the rate of heating of nitrogen, oxygen, and argon plasmas were also carried out. The assumption of coronal equilibrium is not used. It is shown that the low-frequency modulation of the heating power can substantially ease the overcoming of the radiation barrier.

Thermally assisted ECR etching of CdTe in CCl 2F 2/Ar discharge under different gas flow ratio

II–VI compounds have attracted increasing attention, primarily because of the large range of energy band gaps available. ECR plasma etching of CdTe in a CCl 2F 2/Ar discharge with rf biasing were investigated at different temperature and different flow rate ratio. The etch rate increases with the increase in flow rate of reactive gas and temperature. The use of ECR conditions with additional rf biasing provides the good etching of the surface and fast etch rates. The etch depths were measured by Dektek profilometry and the surface morphology with scanning electron microscopy. This paper reports the thermal effect on the etch process of CdTe and the effect of various gas flow rates and ratio between CCl 2F 2 and Ar.

Fabrication and Characterization of NiCr/NiSi Functional Thin Films on Temperature Measurement of Cutter Sensor

NiCr/NiSi functional thin films of temperature measurement of cutter sensor were prepared by means of advanced Twinned microwave ECR plasma source enhanced Radio Frequency (RF) reaction non-balance magnetron sputtering technique. Fabrication technologies of NiCr/NiSi thin films were studied. The Compositions, micro-morphology, general structure and depth of NiCr/NiSi thin films were analyzed by means of Electron Probe, SEM, AFM, step profiler and stereo vision micro operation system. The results showed that NiCr/NiSi thin-films were small depth, uniform compact, smooth and good continuity, composition of which was close to target.

Contributions of the “Saturn” to Modern Stellarator-Torsatron Research

It has been 40 years since the startup and first plasma from the Saturn stellarator-torsatron. The l = 3 stellarator-torsatron “Saturn” was the first of a series of torsatron-like devices built in Kharkov Institute of Physics and Technology (KIPT) in the 1970s: later appeared “Vint-20”, “U-3”, “U-3M”. The Saturn device was used for comparative investigations on the same device two magnetic configurations in stellarator and torsatron regimes and for experimental examination of their effects on plasma confinement. The thorough measurements of magnetic structure in both regimes demonstrated their high equivalence. Investigations of torsatron without toroidal coils supported the principal possibility to have a spatial divertor configuration, which was later realized in U-3, the first torsatron with a divertor. The results on Saturn, obtained for the first time with a pure torsatron configuration, have opened the prospect for torsatrons to be an alternative to tokamaks in the development of a fusion reactor. After various magnetic configurations were studied, the Saturn device was used for providing investigations of confinement of injected hydrogen plasma and of ECR plasma in different gases. In this paper we summarize the main Saturn results and try to find the bridge between them and the present experiments on existing stellarator-type fusion devices with an aim to see what particular Saturn results were supported by those obtained later.

Investigation of mask selectivities and diamond etching using microwave plasma-assisted etching

Diamond etching is characterized using a microwave ECR plasma reactor with regard to etch rate selectivity, surface morphology, and feature size. Etching is performed on diamond substrates using a variety of etch mask materials including aluminum, titanium, gold, silicon dioxide and silicon nitride. The etch feed gases are combinations of oxygen, sulfur hexafluoride and argon. Aluminum masks provided the highest selectivity ratio of diamond etch rate to mask etch rate, both with and without SF 6 in the oxygen/argon feedgas. Selectivity was not found to be dependent on mask feature size. Gold masks produced the least degree of micromasking.

Enhanced confinement in electron cyclotron resonance ion source plasma

Power loss by plasma-wall interactions may become a limitation for the performance of ECR and fusion plasma devices. Based on our research to optimize the performance of electron cyclotron resonance ion source (ECRIS) devices by the use of metal-dielectric (MD) structures, the development of the method presented here, allows to significantly improve the confinement of plasma electrons and hence to reduce losses. Dedicated measurements were performed at the Frankfurt 14 GHz ECRIS using argon and helium as working gas and high temperature resistive material for the MD structures. The analyzed charge state distributions and bremsstrahlung radiation spectra (corrected for background) also clearly verify the anticipated increase in the plasma-electron density and hence demonstrate the advantage by the MD-method.